Hardware maintenance is normally problematic from a logistic and system management perspective. Defective hardware normally will prevent a system from continuing normal operation until the defective parts are replaced or repaired. Finally, hardware management can present a problem for system migration.
In a conventional computer system, the operating system installed on the computer accesses hardware devices directly. The piece of software inside an operating system that communicates with the hardware is known as a device driver. In a virtualized system, the operating system does not access the hardware devices directly; instead it communicates with virtual devices provided by the hypervisor, which in turn communicates with the real hardware. The hypervisor can act as a transparent proxy to the hardware (simply relaying access requests from the operating system), but it can also completely alter the view of the hardware that is presented to the operating system.